This invention relates to single-lens reflex cameras with interchangeable lenses and, more particularly, to an interlocking mechanism for such camera.
A photographic camera incorporating an exposure meter is well known. A desired diaphragm value is selected and preset by operation of a diaphragm preset ring, and then a shutter speed based on the preset value is read from the exposure meter in the camera body so that on the basis of the selected diaphragm value an exposure value in the form of a shutter speed is given as the photometric result of said exposure meter. As an improvement of such photographic camera with exposure meter, so-called automatic exposure control cameras of diaphragm priority type are already commercially available. After a desired diaphragm value has been preset by operation of the diaphragm preset ring, an exposure time of the shutter which is actuated simultaneously with the shutter release is automatically controlled on the basis of an arithmetic result provided from an exposure control circuit according to said preset diaphragm value. Said photographic camera incorporated with the exposure meter and the last-mentioned photographic camera in which the exposure time of the shutter is automatically controlled will be hereinafter generally referred to, for convenience of description, simply as ES camera.
The photographic camera similarly incorporated with the exposure meter but of another type is also well known, in which, instead of presetting a desired diaphragm value, a desired shutter speed and therefore a desired exposure time is preset to avoid blur of the image or movement of hands when an object to be photographed is moving or relatively dark, and then a diaphragm value for proper exposure is read from the exposure meter incorporated in the camera body on the basis of said preset shutter speed value of exposure time value so that the diaphragm is set to this value read from the exposure meter immediately before photographing is actually done. As an improvement of such photographic camera, the so-called automatic exposure control camera of shutter priority type has already been available for many years. In this type of camera, a desired shutter speed is preset and the lens aperture is automatically stopped down on the basis of an arithmetic result provided by the exposure control circuit according to said preset shutter speed when the shutter is actuated by the shutter release. The photographic camera with exposure meter as mentioned in this paragraph and the last-mentioned photographic camera of which the lens aperture is automatically stopped down for the desired exposure control will be hereinafter generally referred to, for convenience of description, simply as EE camera.
A series of such developments to achieve photographing with proper exposure has recently resulted in realization of a photographic camera functioning as both ES camera and EE camera, and correspondingly interchangeable lenses adapted for these both functions have also been proposed. With such interchangeable lenses thus adapted for both ES camera and EE camera, a proper changeover between said two functions in actual use and an operation of this changeover must be as simple as possible. For said operation of changeover, a diaphragm preset ring of each interchangeable lens is provided over a limited angular range therearound not only with graduations for diaphragm presetting but also with a separate set marking for EE camera so that the diaphragm preset ring may be rotated to said separate set marking to adapt the interchangeable lenses for EE camera. In the description of the present invention, the diaphragm preset ring including said set marking for EE camera will be referred to as a diaphragm setting ring.
The interchangeable lenses adapted for both ES camera and EE camera realized through a series of developments as mentioned above have not always been used with a new model of camera having said both types of automatic exposure control function but often used with a photographic camera having automatic exposure control function of either of said two types or a photographic camera of relatively old type with exposure meter.
In this situation, erroneous use of the interchangeable lens with respect to the type of photographic camera on which this interchangeable lens is to be mounted will prevent photographing with proper exposure.
When an interchangeable lens adapted for both ES camera and EE camera is mounted on and used with EE camera, the diaphragm setting ring is rotatably aligned with the automatic diaphragm control position so that the camera automatically performs a desired exposure control and stops down the interchangeable lens mounted on the camera to a proper value. However, unintentional rotation of the diaphragm setting ring out of the automatic diaphragm control position will make the automatic control function of the diaphragm difficult. As a countermeasure to this problem, there have already been proposed various lock mechanisms which hold the diaphragm setting ring at the automatic diaphragm control position and prevent said ring from being displaced out of said position, once the diaphragm setting ring has been set to said position. This means that, when the lens having its setting ring remaining at the automatic diaphragm control position is mounted on an ES camera, the lock mechanism must be unlocked and thereafter the diaphragm setting ring must be properly adjusted to change over the lens from this state to the automatic exposure of diaphragm priority mode. Photographing without such preliminary adjustment will result in an improper exposure. Rotating the diaphragm setting ring from the automatic diaphragm control position to the diaphragm value presetting range and vice versa for change over of the operation between the two functions without relying upon the lock mechanism would require a complicated construction. For example, a pin operatively associated with the diaphragm should be moved together with the diaphragm setting ring within the normal diaphragm value presetting range, while said pin should not follow the movement of the diaphragm setting ring when the latter moves from said normal diaphragm value presetting range to the automatic diaphragm control position, namely, only the diaphragm setting ring should move. This would require an increased number of parts which could not be easily incorporated into a limited space.